The present invention relates generally to an apparatus, a method and a software module for monitoring the state of elevator doors.
Elevator systems include at least one elevator car that is movable in an elevator shaft or freely along a transport device. The elevator car is normally closed by a car door and the elevator shaft is normally closed by a shaft door at each floor.
Mechanical, magnetic, inductive or similar switches are frequently used for monitoring the doors of an elevator system. In addition, optical systems, for example light barriers or light gratings, are used. The elevator control can be supplied with certain information—for example, about the state of the doors—by the above-identified monitoring devices. However, the information content is relatively limited, since a switch is only in a position to indicate, for example, two states (digital information whether the door is open or closed). In order to be able to build up a more complex monitoring system, there is needed, for example, a combination of several switches and light barriers.
For technical reasons, light barriers or light gratings do not function reliably with a door gap of less than 5 cm. This is a disadvantage of those kinds of solutions. In addition, the reaction time amounts to about 65 milliseconds, which in certain circumstances can be too long.
Optical systems, in particular, have certain advantages since, by contrast with mechanical solutions, they operate in a contactless manner and are not subject to any mechanical wear. Unfortunately, even with more complex optical systems such as used in the field of elevators the informational power is limited to a few states. For example, it can be detected whether anybody stands in the door region and movements can be recognized.
Certain optical photosensors even enable detection of three-dimensional images, wherein mechanically moved parts in the form of, for example, mirrors are used. These sensors are complicated and costly.
A system for monitoring elevator doors, which operates with a preprogrammed processor, a digital camera, an analog camera or a video camera, is shown in the PCT Patent Application WO 01/42120. This represents the closest state of the art. The camera delivers a sequence of two-dimensional images, through comparison of which information about the state of the doors is made available. This system operates with outside light that is captured and received by the camera. This leads to problems in situations where the intensity of this outside light changes very significantly—for example, in the case of incidence of sunlight—and thus strongly increases the image brightness. Conversely, the use of such a camera for the stated purpose can also be problematic when the outside light that is present is not sufficient. It is essential for door state monitoring that the monitoring functions safely and reliably in all circumstances. A dependence on outside light is problematic from this viewpoint. According to the above-identified PCT patent application a classic pattern recognition formulation (pattern matching) is used in order to be able to evaluate the sequence of two-dimensional images. A system operating as shown in the PCT patent application with two-dimensional images cannot make a statement about distances. A specific statement with respect to movements and movement directions is possible, in the case of such a two-dimensionally operating system, only by a calculation-intensive reprocessing of the supplied images.
Three-dimensional semiconductor sensors enabling three-dimensional detection of image information are known. Sensors of that kind are known from, for example, the article “Fast Range Imaging by CMOS Sensor Array Through Multiple Double Short Time Integration (MDSI)”, P. Mengel et al., Siemens AG, Corporate Technology Department, Munich, Germany. A further example is described in the article “A CMOS Photosensor Array for 3D Imaging Using Pulsed Lasers”, R. Jeremias et al., 2001 IEEE International Solid-State Circuits Conference, page 252.